A wide variety of electronic devices and systems employ cooling fans in their housings. The cooling fans generate air flow through the housing and across or over heat generating components to prevent overheating and to protect the heat generating components from damage resulting from extreme temperatures. Devices that conventionally use cooling fans include, for example, portable and desktop computers, radios, automobiles, industrial equipment, and communication system infrastructure. Cooling fans typically come in one of two forms: tube axial fans and motorized impeller fans, otherwise known as centrifugal flow fans.
Tube axial fans have blades that force air to move parallel to the shaft about which the blades rotate. Fan blades are typically mounted around a hub that encloses an electric motor. The hub and fan blades, or impeller, are mounted within a shroud that is cylindrical in shape. Tube axial fans are known for high air flows and relatively low operating pressures, and can have an efficiency as high as 65%. At higher pressures, such as in compact electrical devices where components may block axial airflow, tube axial fans decrease in efficiency and are prone to overloading.
Centrifugal flow fans have blades that force air to move in a radial direction relative to the shaft about which the blades rotate. The centrifugal fan blades are also mounted about a hub and can be airfoil blades, straight blades, backward curved blades, backward inclined blades, radial tip blades, forward curved blades, and radial blades. Each blade type results in different performance characteristics of the centrifugal fan. While centrifugal fans can operate at high pressures and can avoid over-loading, they do not provide the high flow rate that axial tube fans can provide.
In many modern devices, size is a significant concern. Electronics such as computers are becoming increasingly compact. The high density of heat generating electronics within these devices and the lack of space for air flow can create unique cooling demands. A cooling fan is needed that can provide high flow rates while also operating efficiently at increased pressures caused by obstructed flow paths.